Polar Regions - page 3

Mars' Polar Regions

When the Martian polar caps were first viewed through telescopes, most scientists believed that they were made of water ice, like the polar caps on Earth. Like Earth, Mars has a North and South Pole. But while Earth's polar ice caps consist solely of water ice, Mars' polar caps are a combination of water ice and carbon dioxide ice. As the Martian seasons change, the carbon dioxide ice sublimates (vaporizes) in summer, revealing the surface, and freezes again in winter. As fall approaches, in each respective hemisphere, clouds begin to form over the polar region and the ice cap begins to grow. In spring, the polar caps recede.

Aside from ice, Mars' polar regions have some interesting geologic features. The north polar dune field is a vast concentration of sand dunes that stretches around the entire north polar cap. In some areas, the sand measures up to 500 km (300 miles) across. When the dunes begin to thaw in spring, dark spots form on their surfaces. The north polar dunes were first seen during the 1972 mapping of Mars by Mariner 9, and they are identical to dunes in Earth's desert regions.

Satellite imagery also shows the presence of polygon-patterned ground in Martian high latitudes. On Earth, polygons typically form in polar regions as a result of repeated freeze and thawing of ground ice. Some scientists believe that polygons on Mars could be an indicator of subsurface water ice.

Just a few decades ago, nobody knew for certain what the Martian surface looked like. But in the 1970s, Mars orbiter and lander missions began producing striking images of Martian geomorphology. Now, satellite imagery and photos enable scientists to see landforms and the shape of the terrain at the Martian poles.

This image of sand dunes in the north polar region of Mars covers an area about 3 km (1.9 miles) across. As the sand dunes begin to defrost in mid-spring, dark spots form on their surfaces. (Image Credit: NASA/JPL/Malin Space Science Systems)

Poles in the Solar System

Say the words South Pole and North Pole and you'll most likely conjure up images of a barren, frozen territory. This is an accurate description of the polar regions on Mars and Earth, but are polar regions on all planets in the solar system alike? Because Mercury is so close to the Sun, could its polar regions be boiling oceans?

Although we know a lot about the poles on Earth and Mars, much less is known about the poles on the other seven planets in our Solar System. But thanks to advanced telescopes and data from spacecraft orbiter missions, scientists are now learning some interesting facts about polar regions on other planets.

Phoenix Landing Site

The Phoenix Mars Lander will touch down in the northern arctic plains of Mars at a site between 65° and 72° North, a region where the Mars Odyssey observed a reservoir of near-surface ground ice.

Given the extreme, cold conditions of polar regions, you might wonder why the Phoenix Mission would choose the arctic plains as a landing site. Actually, many factors make this an ideal location to conduct the Phoenix experiments. First, Phoenix will land during the retreat of the Martian northern polar cap, when soil is first exposed to sunlight after a long winter. The interaction between the ground surface and the Martian atmosphere that occurs at this time is critical to understanding Mars' climate history.

Second, since the sun never sets during the Martian polar summer, Phoenix can take advantage of maximum sunlight, which is essential to the two solar panels that Phoenix will deploy as an energy source for the robotic arm and other instruments. Sunlight is also important for keeping batteries warm, which will store electrical power.

Lastly, the ice-rich soil in the Martian polar regions may be the only place on Mars where microbial life can survive, and sampling in this region could provide researchers with insight into the planet's habitability.

Three potential landing regions (boxes) for the Phoenix Mars Lander are shown. Currently, the Phoenix team is actively working on selecting a landing site. (Image Credit: NASA/UA/Wash. U)

Although the polar regions probably wouldn't be an ideal location for a long-term base during human missions to Mars, due to the long Martian winter (about one Earth year long), they might be the best place to set up a seasonal base during the summer. Scientists now know that there is water at the Martian poles, which would be an important consideration for human missions.

MAPS AND TABLES

DRY ICE

Carbon dioxide is an atmospheric gas made of one carbon atom and two oxygen atoms. In its frozen, solid state, carbon dioxide is known as dry ice. Rather than melting into liquid carbon dioxide, like water ice melts into liquid water, dry ice sublimates directly into carbon dioxide gas when the temperature reaches about -79 degrees C (-110 degrees F).

On Earth, dry ice is produced artificially and then compressed into pellets or block. Since it doesn't melt into a liquid, dry ice is useful for keeping food, biological samples, and other perishables cool. It is also used for producing special effects (dry ice fog), in cloud seeding processes, and as a substitute for sand in sandblasting.

Dry ice is extremely cold - much colder than most freezers. If you hold dry ice, your hand will begin to feel like it's burning, but the dry ice is actually freezing your skin. Heavy gloves should always be worn when handling dry ice. In addition, since carbon dioxide can become concentrated in enclosed spaces, dry ice should only be handled in well-ventilated areas.

Both caps contain a permanent, year-round ice cap made of water ice and a seasonal cap of carbon dioxide ice that forms in winter and disappears in summer. In the northern polar region, the permanent cap is made of water ice, while the southern permanent cap is carbon dioxide ice mixed with water ice.